1. Field of the Invention
This invention relates to circuit interrupters of the type having a bimetallic thermal trip element and a magnetic instantaneous element and, more specifically, to circuit breakers for distribution transformers to control moderate power distribution on feeder circuits.
2. Description of the Prior Art
Transformers used in power distribution systems generally include a protective device which prevents or limits current overload damage to the transformer and its associated apparatus. A completely self-protected transformer includes a circuit interrupter on the secondary or low voltage side to protect against damage due to overload currents. The secondary circuit interrupter disconnects the transformer from its load if the load current becomes dangerously high.
Commonly used circuit interrupters often incorporate a bimetal thermal trip and an instantaneous magnetic trip. Conventional magnetic trip mechanisms are pivotably mounted in order to provide instantaneous action as seen in U.S. Pat. Nos. 3,983,454; 3,860,898; 3,548,358; 3,288,965; and 3,178,535, wherein the armature or magnetic trip arm is pivotally mounted on the casing of the circuit breaker. These magnetic trip elements include a first portion disposed in proximity with the bimetal element so as to be drawn thereto when a high overload current flows through the bimetal element and a second portion which engages a latch mechanism, upon movement of the trip arm, thereby releasing the latch and opening the contacts of the circuit breaker. In U.S. Pat. No. 3,997,857, assigned to the assignee of the present application, the trip arm is integrally secured to the latch mechanism which thereby forms its pivot point.